Hermetic conductive feedthroughs for a semiconductor wafer

ABSTRACT

A glass wafer has an internal surface and an opposing external surface separated by a wafer thickness. A hermetic, electrically conductive feedthrough extends through the wafer from the internal surface to the opposing external surface. The feedthrough includes a feedthrough member having an inner face exposed along the internal surface for electrically coupling to an electrical circuit. The feedthrough member extends from the inner face partially through the wafer thickness to an exteriorly-facing outer face hermetically embedded within the wafer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.14/050,415, filed Oct. 10, 2013, the content of which is incorporated byreference in its entirety.

TECHNICAL FIELD

The disclosure relates to devices having hermetic, electricalfeedthroughs in glass wafers.

BACKGROUND

Electrical feedthroughs provide an electrically conductive pathextending from the interior of a sealed enclosure or housing to a pointoutside the enclosure. The conductive path through the feedthroughincludes a conductor pin, wire or other conductive member or material,which is electrically insulated from the container if the container isformed from a conductive material. For example, a conductive feedthroughin an implantable medical device (IMD) provides an electricallyconductive path from a connection point to electronic circuitrycontained within the IMD enclosure or housing to a point outside theenclosure. The feedthrough member is sealed to the enclosure to preventthe ingress of blood or other body fluids which could damage IMDinternal circuitry and cause device malfunction or failure. The junctionbetween the enclosure and the conductive member of the feedthrough canbe vulnerable to leakage into the IMD enclosure when it is implanted andexposed to body fluids.

An ongoing design goal of IMDs is overall size reduction to promotepatient comfort and facilitate less invasive or minimally invasiveimplantation procedures. As the size is reduced, selection offeedthrough components becomes limited due to small size requirements,and manufacturability of hermetic feedthroughs becomes more challenging.Other devices, such as micro-electro mechanical systems (MEMS) devices,sensors or other miniaturized devices that operate in fluid conditionsmay require hermetic electrical feedthroughs. Accordingly, a needremains for an improved hermetic feedthrough and associated method ofmanufacturing.

SUMMARY

In general, the disclosure is directed towards a hermetic feedthrough ina glass wafer. A glass wafer having a first surface and an opposingsecond surface separated from the first surface by a wafer thicknessincludes a feedthrough member having a first face and a second face, thefirst face exposed along the first surface. The feedthrough memberextends partially through the wafer thickness such that the second faceis embedded within the glass wafer. An electrically conductive trace isat least partially embedded in the wafer extending away from the secondface and electrically coupling the second face to an electricalconnection point located along the second opposing surface.

In one embodiment, a device enclosure includes a recessed packagedefining a cavity for retaining an electrical circuit. A glass lidhaving an internal surface facing the cavity and an opposing externalsurface facing away from the cavity is sealed to the recessed package toenclose the electrical circuit. An electrically conductive feedthroughextends through the glass lid. The feedthrough includes a feedthroughmember having an exteriorly-facing outer face embedded in the glass lidand an inner face. The inner face is electrically coupled to theelectrical circuit. The feedthrough member extends from the inner facepartially through the lid thickness to the outer face that is embeddedwithin the lid. An electrically conductive trace is at least partiallyembedded in the lid and extends away from the outer face. The traceelectrically couples the exteriorly-facing outer face to an electricalconnection point located along the lid external surface.

In another example, a device, which may be an IMD or other deviceoperating in a fluid environment, includes an electrical circuit and ahermetic enclosure having a package and a glass lid sealed to thepackage enclosing the electrical circuit. The enclosure includes afeedthrough in the glass lid. The feedthrough includes a feedthroughmember having an exteriorly-facing outer face and an inner face. Theinner face is electrically coupled to the electrical circuit. Thefeedthrough member extends from the inner face partially through the lidthickness to the outer face that is embedded within the lid. Anelectrically conductive trace is at least partially embedded in the lidand extends away from the outer face. The trace electrically couples theexteriorly-facing outer face to an electrical connection point locatedalong the lid external surface.

A method of manufacturing a hermetic feedthrough in a glass waferincludes depositing an electrically conductive trace along anexteriorly-facing outer face of a feedthrough member extending through abase layer of the glass wafer and embedding the outer face of thefeedthrough member and at least a portion of the electrically conductivetrace within the glass wafer. The glass wafer may be a lid or otherportion of a device enclosure.

These and other examples are disclosed in the following description. Thedetails of one or more aspects of the disclosure are set forth in theaccompanying drawings and the description below. Other features,objects, and advantages will be apparent from the description anddrawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram of an example IMD.

FIG. 2 is a functional block diagram of the IMD shown in FIG. 1.

FIG. 3 is a schematic diagram of an IMD having a glass enclosure and anelectrical feedthrough according to one embodiment.

FIG. 4 is a schematic diagram depicting one method of manufacturing theIMD enclosure shown in FIG. 3.

FIG. 5 is a schematic diagram of a glass lid of an IMD enclosure havinga hermetic electrical feedthrough according to another embodiment.

FIG. 6 is a schematic diagram of the lid shown in FIG. 5 during amanufacturing process.

FIG. 7 is a schematic diagram of another example of a glass wafer havinga hermetic feedthrough and a process of manufacture.

FIG. 8 is a flow chart of a method for manufacturing a glass lid of anIMD enclosure having a hermetic electrical feedthrough.

DETAILED DESCRIPTION

FIG. 1 is a conceptual diagram of an example device 10 that afeedthrough in a glass wafer may be implemented. In the example shownthe device 10 is an IMD but could any of numerous types of devices thatrequire a hermetic feedthrough. IMD 10 is shown embodied as a monitoringdevice having a pair of electrodes 14 and 16 located along an IMDenclosure 12. IMD enclosure 12 encloses electronic circuitry inside IMD10 and protects the IMD circuitry from body fluids.

In some embodiments, enclosure 12 is manufactured using glass wafertechnology. Enclosure 12, when formed of glass, or glass portions incombination with portions formed of other materials, is a sealablehousing forming a hermetic barrier against body fluid ingress that coulddamage electronics packaged within enclosure 12. Electrical feedthroughsprovide electrical connection of electrodes 14 and 16 across thehermetic barrier, provided by enclosure 12, to internal circuitry whenelectrodes 14 and 16 are positioned along the exterior surface ofenclosure 12. Enclosure 12 may be formed of a silicate glass, e.g.borosilicate or aluminosilicate, fused silica, sapphire or other glassmaterial. In some embodiments, enclosure 12 may include an outer coatingover any portion of enclosure 12 to provide desired surfacecharacteristics or features of IMD 10. In some embodiments, a portion ofenclosure 12, such as an enclosure lid, is a glass wafer including oneor more hermetic feedthroughs, and the other portions, for example abase and sidewalls, are formed of metal or a semi-conductor.

IMD 10 may be embodied as an implantable cardiac monitor whereinelectrodes 14 and 16 are used to sense biopotential signals, e.g. ECGsignals. In alternative applications, electrodes 14 and 16 may be usedfor sensing any biopotential signal of interest, which may be, forexample, an EGM, EEG, EMG, or a nerve signal, from any implantedlocation. IMD 10 may additionally or alternatively be configured to useelectrodes 14 and 16 for measuring impedance across electrodes 14 and 16when implanted in a patient's body.

Electrodes 14 and 16 may be formed of a biocompatible conductivematerial, e.g. titanium, platinum, iridium, or other metals or alloysthereof and may include other materials and/or coatings such as titaniumnitride, platinum black or carbon black to improve conductivity orobtain other desired electrical and/or surface properties. Theconfiguration illustrated in FIG. 1 is just one example electrodeconfiguration. In other instances, sensing electrodes 14 and 16 may belocated at other positions along IMD enclosure 12 than the positionsshown in FIG. 1. Furthermore, electrodes 14 and 16 may be carried by amedical electrical lead extending from enclosure 12 and coupled to IMDinternal circuitry via electrical feedthroughs.

A portion of enclosure 12 may function as an electrode and be insulatedfrom any other electrodes positioned along enclosure 12. Althoughillustrated and described as being a cardiac monitor, IMD 10 may be anyof a number of other implantable devices, including implantablehemodynamic monitors, blood chemistry monitors, pressure monitors, nervemonitors, muscle monitors, brain monitors, or the like. In any of thesecases, IMD 10 may include other sensors besides or in addition toelectrodes 14 and 16 to monitor desired physiological signals. In someembodiments, IMD 10 may be configured to deliver a therapy. For example,IMD 10 may be configured to deliver an electrical stimulation therapyvia electrodes 14 and 16.

Moreover, a hermetic feedthrough as disclosed herein is not limited toimplementation in an IMD. Numerous other devices, including MEMSdevices, sensors, or other miniaturized devices for use in a fluidenvironment, which may be within the body of a living subject or otherenvironments, may require a hermetic feedthrough and as such mayimplement a feedthrough as described herein.

FIG. 2 is a functional block diagram of IMD 10 shown in FIG. 1. Invarious embodiments, IMD 10 may include an electrical sensing module 20,an impedance monitoring module 22, and a pulse generator 24. Each ofmodules 20 and 22 may be coupled to electrodes 14 and 16 for sensingelectrophysiological signals and/or monitoring impedance acrosselectrodes 14 and 16. Pulse generator 24, if present, may be coupled toelectrodes 14 and 16 for delivering electrical stimulation pulses to apatient, e.g. for delivering cardiac pacing, nerve stimulation, deepbrain stimulation, or other neurostimulation.

In some embodiments, electrodes 14 and 16 are coupled to the variouscomponents within IMD 10 as required at appropriate times usingswitching circuitry controlled by processing and control module 26. Inother examples, IMD 10 may include dedicated sensing electrodes coupledto sensing module 20 and impedance monitoring module 22 and dedicatedtherapy delivery electrodes coupled to pulse generator 24. More than oneelectrode pair may be provided for sensing additional signals and/orproviding dedicated sensing and therapy delivery electrodes.Feedthroughs 50 and 51, shown schematically, provide electricallyconductive pathways from each of electrodes 14 and 16 located exteriorlyto enclosure 12, e.g. along the outer surface 12 a of enclosure 12, to acomponent of electrical circuitry contained within enclosure 12, e.g.electrical sensing module, impedance monitoring module 22, and/or pulsegenerator 24.

In various examples, IMD 10 may include or be coupled to one or morephysiological sensor(s) 33 for sensing signals other than biopotentialor impedance signals. For example, sensor 33 may be a pressure sensor,acoustical sensor, optical sensor, temperature sensor, or othermechanical, optical, or chemical sensor that resides externally toenclosure 12. Sensor 33 is coupled to a physiological sensing module 32residing internally to enclosure 12. A feedthrough 52 provides anelectrically conductive pathway for electrically coupling sensor 33 tosensing module 32.

IMD 10 is shown to include a communication module 34 coupled to anantenna 35 for wireless data reception and/or transmission. In someexamples, antenna 35 extends from communication module 34 located withinIMD enclosure 12 to a point external to enclosure 12 to receive and/ortransmit signals. A feedthrough 54 provides an electrically conductivepathway from a distal end of antenna 35 to communication module 34.Communication module 34 may be configured to transmit and receivecommunication signals via inductive coupling, electromagnetic coupling,tissue conductance, Near Field Communication (NFC), Radio FrequencyIdentification (RFID), BLUETOOTH®, WiFi, or other proprietary ornon-proprietary wireless telemetry communication schemes.

A power source 30 provides power to IMD circuitry as needed. Powersource 30 may include one or more energy storage devices, such as one ormore rechargeable or non-rechargeable batteries. In one example, powersource 30 is an inductively-coupled, rechargeable power source orinductively-coupled power transfer device. In such instances, powersource 30 contained within enclosure 12 may be electrically coupled toan external antenna 31 for receiving an inductively-coupled powersignal. A feedthrough 56 provides an electrically conductive pathwayfrom antenna 31, which has a distal end exterior to enclosure 12, to thepower source 30.

IMD 10 includes a processing and control module 26 and associated memory28 to control IMD functions including processing signals received fromelectrodes 14 and 16 and other sensors 33 and controlling pulsegenerator 24 and communication module 34.

The various electrodes 14, 16, sensors 33 and antennae 31 and 35illustrate the types of electrical components that may reside exteriorlyto IMD enclosure 12 and require electrical connection to electricalcircuitry contained within enclosure 12. In order to maintain theintegrity of the internal circuitry, enclosure 12 is a hermeticallysealed housing. As such, each of the feedthroughs 50, 51, 52, 54 and 56provide a hermetically sealed, electrically conductive pathway throughthe wall of enclosure 12. Any of the feedthroughs 50, 51, 52, 54 and 56may include a capacitive filter to provide filtering of externalelectromagnetic interference or other electrical noise that maycontaminate electrical signals conducted to internal IMD circuitry viathe respective feedthrough. A capacitor may be included in theintegrated circuitry within enclosure 12 or along an inner surface 12 bof enclosure 12.

The schematic diagram of IMD 10 shown in FIG. 1 is merely one example ofan IMD that includes an electrical circuit or component within enclosure12 (represented by functional blocks in FIG. 2) that is electricallycoupled to at least one electrical component exterior to enclosure 12.Many other types or configurations of IMDs exist which may utilize ahermetic feedthrough as disclosed herein. IMD 10 may be a MEMS device, asensor, a monitor for that receives and processes and/or stores signals,a therapy delivery device, or any combination thereof. Other examples ofIMDs that could be configured to include a hermetic feedthrough asdisclosed herein are generally described in U.S. Publication No.2006/0192272 (Receveur), U.S. Publication No. 2012/0197155 (Mattes) andU.S. 2012/0101540 (O'Brien), all of which are incorporated herein byreference in their entirety.

Feedthroughs 50, 51, 52, 54 and 56 are shown extending through differentsides of enclosure 12, for example a top side, a bottom side and alateral side, in FIG. 2 for the sake of convenience. It is contemplated,however, that the various feedthroughs extending through a wall ofenclosure 12 may alternatively be located along a single common side,such as a lid of the enclosure 12. Generally, feedthroughs extendingthrough a glass portion of an IMD enclosure as disclosed herein may belocated anywhere along the enclosure that is convenient for electricalconnection to the internal device circuitry, convenient for electricalconnection to an external component, such as an antenna, electrode orother sensor or other conductive element and/or simplifies manufacturingmethods.

FIG. 3 is a schematic diagram of a sectional view of an IMD 100 having aglass enclosure 101 and electrical feedthrough 130 according to oneembodiment. Glass enclosure 101 includes a lid 102 and a recessedpackage 104 formed from glass wafers. Recessed package 104 has a bottomside 106 with a lateral sidewall 108 extending upward from andcircumscribing bottom side 106 to define an interior cavity 107.Recessed package 104 may be formed from a glass wafer by etching,sand-blasting, machining or otherwise removing material from the waferto form cavity 107 in some examples.

Recessed package 104 may be a single component or a multi-part componentthat is bonded or fused together. For example, sidewall 108 may bebonded or fused to bottom side 106 in a manufacturing assembly step. IMDcircuitry 105 is located within cavity 107. Recessed package 104 and lid102 are hermetically sealed at junction 116 between lateral side wall108 and lid 102, e.g. by fusion bonding of the glass material or othermethods. If package 104 is formed of another material such as a metal,the junction 116 may be sealed using soldering, brazing or other bondingmethods.

Glass lid 102 is a multi-layer lid including at least a base layer 112having an inner surface 124 facing interior cavity 107 of recessedpackage 104 and a top layer 110 having an external top surface 122facing away from cavity 107. Base layer 112 and top layer 110 arehermetically sealed, e.g. by fusion bonding, along interface 128 to forma combined overall thickness of lid 102 that separates external topsurface 122 from opposing inner surface 124.

Feedthrough 130 extends through lid 102. Base layer 112 includes a via115 defined by interior sidewalls 114 extending from the inner surface124 of base layer 112 to base layer top surface 120, at interface 128between base layer 112 and top layer 110. In the example shown,sidewalls 114 are vertical sidewalls, extending approximatelyperpendicular to inner surface 124 and top surface 120. In otherembodiments, sidewalls 114 may be angled and extend non-perpendicularlyto inner surface 124. A feedthrough member 132 extends through via 115.Feedthrough member 132 is a conductive pin, wire or other conductivematerial filling, or at least partially filling, via 115 and bonded tothe interior sidewalls 114 of base layer 112. Feedthrough member 132 maybe any conductive metal or metal alloy, such as titanium, tungsten,niobium, copper, nickel, gold, platinum, iridium and solders such asPbSn or AuSn.

Feedthrough member 132 is formed of a conductive material that may havea thermal expansion coefficient that substantially matches the thermalexpansion coefficient of base layer 112. Feedthrough member 132 may bedeposited in via 115 as a solid component that is bonded to interiorsidewalls 114, metallized or electroplated within via 115, or otherwisedeposited to fill or partially fill via 115. In one example, feedthroughmember 132 may be a tungsten or titanium member assembled in anappliance. A glass material, e.g. commercially available BOROFLOAT® orB270 Superwite® or other generic glasses as listed herein withoutlimitation, may be heated and flowed around the feedthrough member 132to simultaneously form via 115 and bond feedthrough member 132 to viasidewalls 114.

Feedthrough member 132 has an inner face 134, facing interiorly towardcavity 107, which is electrically coupled to electronic circuitry 105via a conductive path 118. Conductive path 118 may be solder bump orconnector pad that becomes aligned with a connection point on circuitry105 when circuitry 105 is assembled within enclosure 101. The glassmaterial of enclosure 101 may be selected to have a thermal coefficientof expansion that approximately matches the thermal coefficient ofexpansion of a silicon integrated circuit or other component ofcircuitry 105 to allow precise alignment between conductive path 118 anda respective connection point on circuitry 105. Matching thermalexpansion coefficients between enclosure 101 and circuitry 105 enablesreliable flip-chip connections to be made between circuitry 105 andfeedthrough member 132 and protects stress-sensitive components, such asHall-effect sensors or other sensors that may be included in circuitry105.

In past practice, a feedthrough member typically extends entirelythrough an enclosure wall so that one end or face is exposed along aninner surface of the enclosure for electrical connection thereto and theother opposing end or face is exposed along an external surface of theenclosure for electrical connection thereto. In this way, thefeedthrough may be a single continuous path from the inner surface tothe outer surface of the enclosure. A bond between the sides offeedthrough member and the surrounding enclosure material (along the viasidewall) may be exposed to temperature cycling or other thermalchanges. Thermal changes may compromise the bond between the twodifferent materials and thus compromise the hermeticity of the enclosurewhen the feedthrough member is exposed to an external fluid environment.

In feedthrough 130, the exterior-facing outer face 136 of feedthroughmember 132 is embedded in lid 102, between top layer 110 and base layer112. An electrically conductive trace 138 extends from the feedthroughmember outer face 136 to an open cavity 125 defined by interiorsidewalls 126 of top layer 110. Open cavity 125 is open to the exteriorof enclosure 101 and open to the top surface 120 of base layer 112,thereby exposing a portion of trace 138.

Trace 138 may be a thin film or layer of any electrically conductivematerial. In an IMD, trace 138 may be a biocompatible, biostableconductor such as titanium, niobium, tantalum, platinum or alloysthereof. In some embodiments, trace 138 may extend within a grooveformed along top layer 110 and/or base layer 112 at interface 128 tomaintain a level surface for bonding between top layer 110 and baselayer 112.

Trace 138 is exposed in cavity 125 to provide an electrical connectionpoint 150 for electrically coupling an external electrically conductivemember 140 to feedthrough member 132. Electrically conductive member 140may be a coupling member or contact pad to which an electrode or othersensor, antenna, or other external component is directly or indirectlyelectrically coupled. In some embodiments, an electrode or otherexternal component may be mechanically coupled to top layer 110 withincavity 125 or along external top surface 122.

In various embodiments, conductive member 140 may wholly fill all ofcavity 125 such that an electrode, sensor or other electrical componentcan be coupled to member 140 and extend along or away from external topsurface 122 and enclosure 101. In other embodiments, conductive member140 may fill a portion of cavity 125 and an electrode, sensor or otherelectrical component may fill the remainder of cavity 125 to extendflush with top surface 122 or protrude from top surface 122. In someembodiments, conductive member 140 is an electrode that fills cavity 125and is directly coupled to trace 138 at connection point 150 without aseparate coupling member. The cavity 125 provides a recess for retainingan electrode that is flush with or below top surface 122. By positioningan electrode or other sensor flush with or below top surface 122, thesensor is protected from tools or other handling or delivery objectsduring manufacturing and implantation procedures.

By embedding outer face 136 of feedthrough member 132 within lid 102,the bond between feedthrough member 132 and sidewalls 114 of via 115 isnot directly exposed to body fluids or other external environment. Outerface 136 of feedthrough member 132 and at least a portion of trace 138are embedded within lid 102 between top layer 110 and base layer 112when layers 110 and 112 are fusion bonded along interface 128. Byhermetically sealing outer face 136 and at least a portion of trace 138within lid 102, the bond between sidewall 114 and feedthrough member 132is protected from exposure to body fluids and the ingress of body fluidsinto enclosure cavity 107 along a path through feedthrough 130 is highlyunlikely.

In the example shown, the feedthrough 130 does not include a ferrule.The feedthrough member 132 is bonded directly to the interior sidewall114 of enclosure lid base layer 112. In other examples, a ferrule orother intermediate layer or coating may be used between feedthroughmember 132 and interior sidewall 114 to enhance sealing betweenfeedthrough member 132 and sidewall 114.

In the illustrative embodiments described herein, a hermetic feedthroughis shown extending through a lid of an IMD enclosure. It is contemplatedthat the IMD enclosure may have one or more feedthroughs extendingthrough the lid 102 and/or a wall of the recessed package 104 of theenclosure. Furthermore, it is contemplated that lid 102 may be recessedalong inner surface 124 such that lid 102 also forms a portion of theinterior cavity 107. For example, recessed package 104 and lid 102 maybe symmetrical.

FIG. 4 is a schematic diagram depicting one method for use inmanufacturing enclosure 101 shown in FIG. 3. Lid 102 is assembled from aglass wafer top layer 110 and a glass wafer base layer 112. Base layer112 includes a via 115 defined by an interior vertical sidewall 114extending from lid inner surface 124 to a top, exterior-facing surface120 of base layer 112. Feedthrough member 132 extends through via 115from an inner face 134, which may be recessed from, flush with orprotrude from inner surface 124, to an outer face 136 that is flush withtop surface 120 of base layer 112. In various embodiments, solder bumpsor other connection points may be provided along the inner face 134 offeedthrough member 132.

An electrically conductive trace 138 is deposited or printed along topsurface 120 of base layer 112 in direct electrical contact with outerface 136 of feedthrough member 132. Trace 138 extends from a first end144 directly coupled to outer face 136 of feedthrough member 132 to asecond end 146 terminating within cavity 125 defined by top layer 110.In various embodiments, trace 138 may extend entirely across a width ordiameter of top face 136 or less than a full width or diameter of topface 136. Trace 138 may extend across a full width or diameter of cavity125 or a portion thereof.

Top layer 110 is fusion bonded or otherwise sealed to base layer 112along base layer top surface 120. The top face 136 of feedthrough member132, trace first end 144 and a portion of the mid-section of trace 138that extends between the first end 144 and second end 146 are embeddedbetween the top layer 110 and base layer 112 upon bonding the two layers110 and 112 together. The distal end 146 of trace 138 is exposed withincavity 125 to provide an external electrical connection point 150, alongthe exposed portion of trace 138, to facilitate electrical coupling tofeedthrough member 132. The electrical connection point 150 is laterallyspaced apart from feedthrough member 132 and separated from feedthroughmember outer face 136 by a hermetic bond between layers 110 and 112.

Top layer 110 is ground or machined down to a desired thickness and toexpose cavity 125. A portion of top layer 110 is removed down to atleast the recessed lateral surface 137 of cavity 125, e.g. down todashed line 142, to open cavity 125 to the external environment. In someembodiments, the entire top surface 148 of top layer 110 is removed downto dashed line 142 to expose cavity 125 and form an open cavity as shownin FIG. 3. In other embodiments, only a portion of top layer alignedwith cavity 125 may be removed from top surface 148 to extend cavity 125by forming an opening in top surface 148, e.g. by laser drilling,thereby exposing cavity 125. Electrically conductive member 140 (shownin FIG. 3) may then be deposited or assembled in cavity 125 through atop opening of cavity 125, e.g. by metallization of the exposed topsurface 120 of base layer 112. In other embodiments, conductive member140 could be assembled or deposited into cavity 125 of the top layerglass wafer prior to bonding top layer 110 to base layer 112 and beforegrinding top surface 148.

In another example, cavity 125 may extend entirely through top layer 110and may be previously formed through a glass wafer by laser drilling,sand-blasting or other removal methods to form top layer 110 with opencavity 125 defined by interior sidewall 126 prior to bonding to baselayer 112. In each of these examples, however, connection point 150 oftrace 138 is ultimately exposed to the outer environment surroundingenclosure 101 while feedthrough member top face 136 is embedded withinlid 102 without being directly exposed to the exterior environment andwithout having an external component coupled directly to the feedthroughmember 132. An external component, such as an antenna, electrode orother sensor, is only indirectly coupled to feedthrough member 132 viatrace 138. The connection point 150 to trace 138 is along the externaltop surface 122 of lid 102 and spaced apart laterally from the embeddedouter face 136 of feedthrough member 132. Via 115 extends only partiallythrough lid 102 such that via 115 is terminated below the lid externaltop surface 122.

FIG. 5 is a schematic diagram of a glass lid 202 of an IMD enclosurehaving a hermetic electrical feedthrough 230 according to anotherexample. Glass lid 202 is formed from a glass wafer top layer 210 and aglass wafer base layer 212. Feedthrough 230 extends from an innersurface 224 of lid 202 to an external top surface 222. Feedthrough 230includes a first feedthrough member 232 a extending partially throughlid 202 and a second feedthrough member 232 b extending partiallythrough lid 202 and laterally displaced from first feedthrough member232 a. First and second feedthrough members 232 a and 232 b areelectrically coupled by a conductive trace 238 a and 238 b, collectively238, embedded in lid 202, along interface 228 between top layer 210 andbase layer 212.

First feedthrough member 232 a extends between an exterior-facing, outerface 236 a embedded within lid 202 and an interior-facing inner face 234a exposed along lid inner surface 224. Feedthrough member 232 a isbonded to interior sidewall 214 a defining via 215 a. Via 215 a extendsfrom lid inner surface 224 only partially through lid 202, terminatingbeneath lid external surface 222, e.g. at interface 228 between baselayer 212 and top layer 210.

Second feedthrough member 232 b is laterally offset (spaced apart) fromfirst feedthrough 232 a. Second feedthrough member 232 b has aninterior-facing inner face 234 b embedded within lid 202 and anexterior-facing outer face 236 b exposed along lid external top surface222. Outer face 236 b of second feedthrough member 232 b provides anelectrical connection point 250 that is along the external top surface222 of lid 202, opposite lid inner surface 224. When lid 202 is providedas part of an enclosure of an IMD, connection point 250 is a biostable,biocompatible surface. For example, feedthrough member 232 b may beformed of titanium, tantalum, platinum, iridium or alloys thereof. Insome embodiments, biocompatibility and biostability of connection point250 may be improved by coating feedthrough member 232 b, e.g. withcarbon black, platinum black, platinum sputtering, titanium nitride orother coating.

Via 215 b, defined by interior sidewall 214 b, extends from lid externaltop surface 222 only partially through lid 202, terminating above lidinner surface 224, e.g. at interface 228 between base layer 212 and toplayer 210. A central axis of via 215 a and corresponding feedthroughmember 232 a is laterally offset from a central axis of via 215 b andcorresponding feedthrough 232 b. Feedthrough members 232 a and 232 b arealso vertically offset through lid 202 in that members 232 a and 232 bdo not overlap each other in any horizontal plane extending through lid202 parallel with inner surface 224 and external top surface 222.

Electrically conductive trace 238 is embedded within lid 202 alonginterface 228 and extends from embedded inner face 234 b of feedthrough232 b to embedded outer face 236 a of feedthrough 232 a. Trace 238 maybe deposited or printed along the top surface of base layer 212 and/orthe bottom surface of top layer 210 such that when top layer 210 is]bonded to base layer 212, trace 238 is embedded within lid 202. In someembodiments, trace 238 may include two or more overlapping or partiallyoverlapping traces 238 a and 238 b located along the top surface of baselayer 212 and the bottom surface of top layer 210, respectively. Trace238 may be a thin film to add negligible thickness along interface 228.

FIG. 6 is a schematic diagram of lid 202 during a manufacturing process.Top layer 210 and bottom layer 212 may be formed from identical glasswafers having feedthrough members 232 a and 232 b extending completelythrough the respective wafers and traces 238 a and 238 b extending alongone surface of each of the wafers, as shown in top panel A of FIG. 6.The wafer that becomes top layer 210 in lid 202 is flipped end-over-endby rotating the wafer in a direction indicated by arrow 242 on a z-axis,indicated by “x” 240, extending perpendicularly into the page.

The traces 238 a and 238 b are in overlapping, facing alignment as shownin panel B after flipping the top wafer in the manner described above.Feedthrough members 232 a and 232 b are no longer aligned with a commoncentral axis. Feedthrough members 232 a and 232 b are laterally spacedapart from each other.

The top wafer that becomes top layer 210 and the bottom wafer thatbecomes base layer 212 are positioned against each other and fusionbonded or otherwise hermetically joined along interface 228 to form thebi-layer lid 202 shown in panel C. The bi-layer lid 202 has feedthrough230 including two, laterally spaced apart feedthrough members 232 a and232 b each having opposing outer and inner faces 236 a and 234 b,respectively, embedded within lid 202 along the hermetic interface 228.Traces 238 a and 238 b are aligned and overlap to form trace 238 thatelectrically couples feedthrough members 232 a and 232 b. Trace 238 isentirely embedded within hermetically fused interface 228 in thisembodiment, but electrically couples feedthrough member 232 a to anexternal connection point 250 by way of feedthrough member 232 b.

A desired overall thickness of lid 202 may be achieved by grinding downthe glass wafer that becomes top layer 210 to form lid external topsurface 222. As shown in panel C, top layer 210 may have a finalthickness that is less than the thickness of base layer 212.

The thickness of trace 238 is exaggerated in the drawings shown hereinfor the sake of clarity; it is recognized that trace 238 would be verythin such that it lies substantially flat along interface 228. Forexample trace 138 shown in FIG. 3 and trace 238 shown in FIG. 5 may beon the order of angstroms to microns thick while respective lids 102 and202 may be approximately 3 millimeters or less in thickness. In someexamples, lids 102 and 202 may be less than 1 millimeter in thickness,e.g. about 0.5 millimeters in thickness. The base layer 112 may beapproximately 0.5 millimeters in thickness and the top layer 110 may beon the order of approximately 50 to 100 microns in thickness. In someexamples given herein, the term “approximately” refers to a value within10% of a stated value.

FIG. 7 is a schematic diagram of another example of a glass wafer havinga hermetic feedthrough and an associated process of manufacture. Anelectrically conductive trace 338 is deposited on a top surface 320 of aglass wafer base layer 312 as shown in panel A. The trace 338 may betitanium, tungsten, tantalum, platinum, iridium, or other biocompatible,biostable metal or alloy thereof and may be printed, sputtered,metallized, electroplated or deposited using an evaporation process.

A wafer top layer 310 is bonded to the top surface 320 of base layer 312(panel B) to hermetically seal top layer 310 to base layer 312, e.g. byfusion bonding. Trace 338 is embedded within the hermetic interface 328formed between top layer 310 and base layer 312. In some embodiments acoating may be provided along the interface 328 to enhance bondingand/or planarize the top surface 320 after depositing trace 338 toimprove the hermetic seal between top layer 310 and base layer 312. Forexample, in this and other embodiments disclosed herein, a coating ofSilox or Teos (tetraethyl orthosilicate) or other binding sealant may beapplied to top surface 320 of base layer 312 after positioning trace 338along the top surface 320 using any of the methods listed above inpreparation for bonding the two layers 310 and 312.

As shown in panel C, an inner via 315 a and an outer via 315 b areformed in the base layer 312 and top layer 310, respectively, byetching, laser drilling, or other removal method to form sidewalls 314 aand 314 b defining the vias 315 a and 315 b which both extend down totrace 338. Any non-conductive coating applied over trace 338 forplanarization or other purposes may be etched away at least in a portionthat will become exposed at the base 316 b of via 315 b. In otherexamples, vias 315 a and 315 b are formed through layers 312 and 310,respectively, prior to bonding the layers together.

Feedthrough members 332 a and 332 b are deposited in vias 315 a and 315b, respectively (panel D) to form a glass wafer lid 302 having ahermetic feedthrough 330. Feedthrough members 332 a and 332 b may beformed by sputtering, electroplating, or other metallization techniquesor combinations of techniques. In some embodiments, feedthrough members332 a and/or 332 b may include a sputtered layer and a plated layer. Topsurface 322 may be ground down to achieve a desired overall thickness oflid 302.

Sidewalls 314 a and 314 b are shown angled in this embodiment, which mayfacilitate metallization, sputtering or other processes used to depositfeedthrough members 332 a and 332 b in vias 315 a and 315 b. In variousembodiments, a feedthrough member is deposited as a film or layer alongat least the base of the via and may extend up the via sidewall. As anexample, feedthrough member 332 b is shown along base 316 b of via 315 bproviding an external contact point 350 for electrical coupling to anembedded exteriorly-facing outer face of feedthrough member 332 a. Thefeedthrough member 332 a extends along via 315 a along its base 316 a,sidewall 314 a and out of via 315 a along inner surface 324 of baselayer 312. The extent that feedthrough members 332 a and 332 b extendalong via sidewalls 314 a and 314 b and inner surface 324 or externaltop surface 322 may vary between embodiments and may depend on whatexternal electrical components are being coupled to feedthrough 330,their location relative to feedthrough 330, and methods used forcoupling to an electrical circuit housed by an associated enclosure ofwhich lid 302 is a portion. For example, portions of feedthrough member332 a that extend along inner surface 324 may provide electricalcoupling points 351 for electrically coupling to an electrical circuitthat will be enclosed in a hermetic enclosure.

When feedthrough members 332 a and 332 b extend along external topsurface 322 or inner surface 324, non-conductive coatings may be appliedover a portion of the feedthrough member to define a conductiveelectrode or contact pad area. For example, a coating of parylene,silicone, deposited glass or other non-conductive coating may be appliedto define insulated and non-insulated portions of feedthrough member(s)332 a and/or 332 b.

FIG. 8 is a flow chart 400 of a method for manufacturing an IMDenclosure having a hermetic electrical feedthrough according to oneexample. At block 402, a via is formed in a glass wafer that will becomea base layer of a lid of the enclosure. A via hole in a glass wafer maybe formed by laser drilling or sandblasting. The via is defined by aninterior sidewall, which may be vertical or angled, formed in the glasswafer at a desired location. At block 404 a conductive feedthroughmember is deposited in the via. For example, the feedthrough member maybe any conductive metal such as titanium, tungsten, niobium, copper,nickel, gold, platinum, and solders such as PbSn or AuSn. Thefeedthrough member may be deposited in the via by electroplating,metallization, as a solid pre-formed member or other deposition methods.In some examples, via formation at block 402 and deposition of thefeedthrough member at block 404 is achieved in a single step bypositioning the feedthrough member, e.g. a titanium or tungsten pin, inan assembly and flowing the glass material of the glass wafer around thefeedthrough member.

An electrically conductive trace is deposited along a top surface of theglass wafer at block 406, e.g. by printing, sputtering, evaporating,electroplating or other methods, so that the trace extends along anexposed outer face of the feedthrough member. At block 408, the glasswafer is bonded with a second glass wafer that becomes the top layer ofthe lid. The outer face of the feedthrough member in the base layer andat least a portion of the conductive trace deposited on the top surfaceof the base layer are embedded in the bonded interface between the twoglass wafers. In some examples, as shown in FIG. 7, embedding aconductive trace in a layered glass wafer may be performed prior toforming a via and depositing a feedthrough member in the via.Accordingly, the particular order of the blocks shown in FIG. 8 are notintended to convey any limitations regarding a particular order of stepsperformed in a manufacturing process but merely indicate processes andaspects of steps that are included to arrive at a glass wafer having ahermetic feedthrough extending from an inner wafer surface to anopposing external top wafer surface and including an embeddedfeedthrough member face.

An external component is coupled to the embedded feedthrough member facevia the trace at block 410. The external component, e.g. an electrode orother sensor, may be assembled onto an external connection pointprovided by the trace. In some embodiments, an external component may bea metallized contact pad or other component. In some examples, e.g. asshown in FIG. 4, a cavity is formed in the second glass wafer, e.g. bysand blasting, laser drilling or machining, that extends partiallythrough the second glass layer. The cavity is aligned with a portion ofthe trace but is laterally offset from the embedded outer face of thefirst feedthrough member. Upon fusing or bonding the two glass waferstogether, a portion of the trace is exposed within the cavity of thesecond wafer providing an external electrical connection point while theremainder of the trace is embedded within the hermetically bondedinterface, extending laterally toward the embedded feedthrough outerface.

A top surface of the wafer may be ground down to create open access tothe cavity and the connection point along the exposed portion of thetrace. The exposed portion of the trace is an external connection pointenabling electrical connection to the embedded face of the feedthroughmember. The connection point is spaced apart laterally from the embeddedexteriorly-facing outer face of the feedthrough member by the trace thatextends laterally along the fused interface away from embeddedfeedthrough outer face. The feedthrough member extends only through theglass wafer forming the lid base layer, from the inner surface of thelid to a top surface of the base layer.

In another example, a second feedthrough member is deposited in a viaformed in the second glass wafer that becomes the lid top layer to makeelectrical contact with the trace upon fusing the first base layer waferto the second top layer wafer. The second feedthrough member may extendfrom a bottom surface of the top layer to the lid external top surfaceand is spaced apart laterally from the embedded outer face of the firstfeedthrough member. The exposed external face of the second feedthroughmember is an external connection point for electrically coupling anexternal component, e.g. an electrode, contact pad, sensor or otherelectrically conductive member, to the embedded face of the firstfeedthrough member by an electrical path including the secondfeedthrough member and the trace. An interiorly-facing inner face of thesecond feedthrough member in the top glass wafer becomes embedded withinthe lid upon fusing the two glass wafers. The second glass wafer may beidentical to the first glass wafer as shown in the example depicted inFIG. 6.

The top glass wafer may be ground down to a thickness that is less thanthe thickness of the bottom glass wafer to achieve a desired lidthickness. The second feedthrough member may be deposited in the cavityof the second glass wafer before or after grinding the top layer down toa desired thickness.

The lid is sealed to a recessed package at block 412. The package may beformed from the same glass material as the lid or another material, e.g.silicon, metal or other biocompatible material. For example, the lid andthe package may both be cut from a silicate glass wafers, sapphire, orfused silica. In other examples, the package may include a semiconductormaterial or a metal. Appropriate sealing techniques are used at block412 according to the material(s) of the package and lid. If both thepackage and the lid are glass, they may be fusion bonded. In someexamples, a coating or interlayer may be applied at the interfacebetween the lid and the recessed package to facilitate formation of areliable hermetic seal.

A hermetic cavity is defined by the sealed glass lid and package forretaining and protecting an electrical circuit. The glass lid has aninternal surface facing the cavity and an opposing external surfacefacing away from the cavity and separated from the internal surface bythe lid thickness. Solder bumps or other connection pads may be appliedat the bottom face of the lid base layer in contact with the feedthroughmember to facilitate connection to an electrical circuit to be containedwithin the enclosure.

In some examples, the electrical circuit is assembled onto the internallid surface prior to sealing the lid to the package. When the lid ispositioned over the recessed package, the electrical circuit ispositioned within the recessed package. In other examples, solder bumpsor other electrical contacts make electrical connection to an electricalcircuit already residing within the recessed package upon placing thelid on the package.

The external connection point of the lid enables an external electricalcomponent to be electrically coupled to the internal electrical circuit.For example, an electrode or other sensor may be electrically coupled tothe external connection point, before or after sealing the lid to thepackage, which becomes electrically coupled to the electrical circuitassembled onto the internal surface of the lid or when the lid is sealedin place onto the recessed package. The enclosure manufactured with aglass wafer lid having a hermetic feedthrough can be incorporated into awafer fabrication processes, using wafer fab tools, processes andmaterials which can significantly improve IMD reliability and reducemanufacturing cost.

Thus, various embodiments of a glass wafer having a hermetic feedthroughhave been described. However, one of ordinary skill in the art willappreciate that various modifications may be made to the describedembodiments without departing from the scope of the claims. Suchmodifications may include altering the order of manufacturing stepsperformed or combinations of features an enclosure, glass wafer and/orfeedthrough in different combinations than those shown and describedherein. These and other examples are within the scope of the followingclaims.

What is claimed is:
 1. A method for manufacturing a hermetic feedthroughin a glass wafer, the method comprising: depositing a first feedthroughmember in a via in a base layer of a glass wafer, wherein a top surfaceof the base layer defines an internal surface of the glass wafer;depositing an electrically conductive trace along the top surface of thebase layer so that the trace and an exteriorly-facing outer face of thefirst feedthrough member are in direct electrical connection; depositinga second electrically conductive trace on a bottom surface of a toplayer, wherein a top surface of the top layer defines an externalsurface of the glass wafer; embedding the exteriorly-facing outer faceof the first feedthrough member and at least a portion of theelectrically conductive trace and the second electrically conductivetrace in the glass wafer such that the electrically conductive trace andthe second electrically conductive trace overlap, wherein embedding theexteriorly-facing outer face of the first feedthrough member comprisesfusion bonding the top surface of the base layer to the bottom surfaceof the top layer along an interface; and electrically coupling theexteriorly-facing outer face of the first feedthrough member to anelectrical connection point located along the external surface of theglass wafer by the electrically conductive trace and the secondelectrically conductive trace extending away from the embeddedexteriorly-facing outer face.
 2. The method of claim 1, furthercomprising positioning the electrical connection point spaced apartlaterally from the embedded exteriorly-facing outer face of the firstfeedthrough member.
 3. The method of claim 1, further comprisingdepositing the first feedthrough member in the base layer to extend fromthe internal surface of the glass wafer to the top surface of the baselayer.
 4. The method of claim 1, further comprising: forming an interiorsidewall in the top layer that defines a cavity that extends from thewafer external surface to the bottom surface of the top layer; andexposing an end of the electrically conductive trace or the secondelectrically conductive trace within the cavity.
 5. The method of claim4, further comprising positioning a sensor in the cavity andelectrically coupling the sensor to the electrically conductive traceand the second electrically conductive trace.
 6. The method of claim 5,further comprising depositing a second feedthrough member in the toplayer extending from the bottom surface of the top layer to the waferexternal surface, the second feedthrough member spaced apart laterallyfrom the first feedthrough member; and electrically coupling the firstfeedthrough member and the second feedthrough member utilizing theelectrically conductive trace and the second electrically conductivetrace.
 7. The method of claim 6, further comprising embedding aninteriorly-facing inner face of the second feedthrough member within theglass wafer.
 8. The method of claim 6, further comprising electricallycoupling an external component to the embedded face of the firstfeedthrough member via an exposed external face of the secondfeedthrough member.
 9. The method of claim 8, wherein the externalcomponent comprises at least one of an electrode, contact pad, orsensor.
 10. The method of claim 6, further comprising grinding the toplayer to a first thickness after depositing the second feedthroughmember in the top layer, wherein the base layer has a second thicknessgreater than the first thickness.
 11. The method of claim 1, furthercomprising grinding the top layer to a first thickness, wherein the baselayer has a second thickness greater than the first thickness.
 12. Themethod of claim 1, further comprising forming a via in the base layerprior to depositing the first feedthrough member in the via in the baselayer.
 13. The method of claim 12, wherein forming the via compriseslaser drilling or sandblasting the base layer to form the via.
 14. Themethod of claim 1, wherein depositing the first feedthrough membercomprises electroplating or metallizing the first feedthrough member inthe via in the base layer.
 15. The method of claim 1, wherein depositingthe first feedthrough member comprises positioning a solid pre-formedmember in the via in the base layer.
 16. The method of claim 1, whereindepositing the electrically conductive trace comprises printing,sputtering, evaporating, or electroplating the electrically conductivetrace along the top surface of the base layer so that the trace and theexteriorly-facing outer face of the first feedthrough member are indirect electrical connection.
 17. The method of claim 1, furthercomprising depositing solder bumps at the bottom surface of the baselayer and in contact with the first feedthrough member.
 18. A method formanufacturing an implantable medical device that comprises a recessedpackage and a glass lid, the method comprising: forming the glass lid,comprising: depositing a first feedthrough member in a via in a baselayer of a glass wafer, wherein the base layer defines an internalsurface of the glass wafer; depositing an electrically conductive tracealong the internal surface of the glass wafer so that the trace and anexteriorly-facing outer face of the first feedthrough member are indirect electrical connection; embedding the exteriorly-facing outer faceof the first feedthrough member and at least a portion of theelectrically conductive trace in the glass wafer, wherein embedding theexteriorly-facing outer face of the first feedthrough member comprisesfusion bonding the base layer to a top layer along an interface, whereinthe top layer defines an external surface of the glass wafer; andelectrically coupling the exteriorly-facing outer face of the firstfeedthrough member to an electrical connection point located along theexternal surface of the glass wafer by the electrically conductive traceextending away from the embedded exteriorly-facing outer face.
 19. Themethod of claim 18, further comprising sealing the glass lid to therecessed package to form an enclosure.
 20. The method of claim 19,further comprising: disposing electrical circuitry within the enclosure;and electrically coupling the electrical circuitry to the firstfeedthrough member.